"The Three Cards Problem": Solution
Solution to The Three Cards Problem, from Wednesday:
The probability is 2/3 that the other side is also black.
There are six faces. Of the three black faces, 2/3 are on the black/black card. So if you're presented with a black face, chances are 2 in 3 that it's on the black/black card — and thus that the card's other side is black.
See also Boy Trouble and The Monty Hall Problem.
